http://ilyusha.myweb.hinet.net/xiiplanet.htm Planetary Definition 行星的定义 根据2006年8月16日，国际天文联合会IAU 共同开会提出的”新行星定义草案” According to the new draft definition, two conditions must be satisfied for an object to be called a "planet." 有以下几点 ( 中文释义转自”台北天文馆新闻” ) IAU将在8/24决定行星的定义，可能改变太阳系家族成员的定位 (1) First, the object must be in orbit around a star, while not being itself a star. 第一，必须环绕一颗恒星运行，而且其自身既不能是恒星，也不能是某个行星的卫星。也就是说，他们挑选了「重力」作为最基本的行星科学定义物理因子，让自然界自行决定何者为行星。 (2) Second, the object must be large enough (or more technically correct, massive enough) for its own gravity to pull it into a nearly spherical shape. 第二，行星的质量应该大到足以使其因自身的重力可和刚体的力维持流体静力平衡（hydrostatic equilibrium）的状态，简单地说，就是可以维持「圆球形」 The shape of objects with mass above 5 x 1020 kg and diameter greater than 800 km would normally be determined by self-gravity, but all borderline cases would have to be established by observation. 符合条件的行星可能同时也应具有 (1) 超过 5 x 1020 公斤的星球质量 (2) 直径起码 800 公里 真实的定义范围还待更进一步的观测确认！ The 12 Planets 十二新定义行星 If the proposed Resolution is passed, the 12 planets in our Solar System will be Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon and 2003 UB313. The name 2003 UB313 is provisional, as a "real" name has not yet been assigned to this object. A decision and announcement of a new name are likely not to be made during the IAU General Assembly in Prague, but at a later time. The naming procedures depend on the outcome of the Resolution vote. 如果前述的草案决议通过，我们的太阳系的12大行星将会是水星、金星、地球、火星、榖神星、木星、土星、天王星、海王星、冥王星、夏隆、2003 UB313。其中2003 UB313的真实名称尚未决定。一个新的名称与发布无法同时在国际天文联合会上进行，但是最後命名的结果넊N会取决於投票。 ※事後将会由命名委员给予一个新的名称！ ※2003 UB313 的发现者Mike Brown团队，给予2003 UB313 ”Xena”的昵称。 There will most likely be more planets announced by the IAU in the future. Currently a dozen "candidate planets" are listed on IAU's "watchlist" which keeps changing as new objects are found and the physics of the existing candidates becomes better known. The draft "Planet Definition" Resolution will be discussed and refined during the General Assembly and then it (plus four other Resolutions) will be presented for voting at the 2nd session of the GA 24 August between 14:00 and 17:30 CEST. 在未来，国际天文联合会会宣布更多的行星，目前还有十数颗行星的候选者列在观察员名单上。 行星新定义的草案决议与其他四项议案将在中欧夏令时间8月24日的14:00～17:30经由大会会员第二次开会投票！ --------------------------------------------- The Plutons 类冥王星星体与行星分类 The IAU draft Resolution also defines a new category of planet for official use: "pluton". Plutons are distinguished from classical planets in that they reside in orbits around the Sun that take longer than 200 years to complete (i.e. they o rbit beyond Neptune). 这次新定义行星草案中使用了新的名词”类冥王星行星”( 冥王星型行星 )。以类冥行星与古典行星区分，是因为它们所在的轨道 ( 绕行轨道於海王星之外 ) 公转太阳周期大多超过200年以上， Plutons typically have orbits that are highly tilted with respect to the classical planets (technically referred to as a large orbital inclination). Plutons also typically have orbits that are far from being perfectly circular (technically r eferred to as having a large orbital eccentricity). All of these distinguishing characteristics for plutons are scientifically interesting in that they suggest a different origin from the classical planets. 类冥行星轨道通常较古典行星倾角较高，而且轨道接近於椭圆 ( 轨道偏心率大 ) ，所以类冥行星的一些特别性质与来源与古典行星不同。故有此新的分类！ -- Because the Kocmoc is so ~ I will explain everything one day ! By iLyuSha -- ※ Origin: 星空之子 <starkids.twbbs.org> ※ From : 218-168-36-44.dynamic.hinet.net